Historically, stretching the fabric screen and attaching the screen to a frame, achieving the appropriate tension, was a time-consuming job, and success was largely dependent upon the skill of the person involved, in that the stretching was done manually and the screen was then attached to a rigid frame mechanically.
As popularity of silk screen process has grown and the need for reduced cost become apparent, silk screen frames were developed wherein the sides of the rectangular frame were elongated cylinders and the screen was attached to the cylinders, then the cylinders were rotated to achieve the appropriate tension. This method likewise required a certain amount of skill and an expensive instrument (tension meter) to ascertain the proper tension. Industry studies indicated that even though the roller frames were relatively rigid, the higher tension achievable with modern fabrics caused inward deflection; and subsequently, the industry started pretensioning and pre-forming the fabrics with integral framework or splines along the edges of the fabric, such that they could be quickly secured to a roller frame by placing the splines in a slot in the roller and tensioned by rotating the cylindrical sides, achieving an equal tension throughout the screen.
The problem still remained in terms of rotating the frame elements in an exact amount to have the appropriate tension. Hence, the present invention incorporates a preformed screen placed upon a pre-positioned frame element and then rotated a predetermined amount. The predetermined amount of rotation is physically placed upon the wrench element in the form of a physical stop means which prescribes the rotation of the roller.
Patents known to the inventor dealing with the process of stretching a fabric on a frame include U.S. Pat. No. 2,832,171 granted to Batey on Apr. 29, 1958, which utilizes two adjacent rollers in a rectangular frame which are interlinked and torqued to create tension on a fabric for a rug; U.S. Pat. No. 4,525,909 granted to Newman on Jul. 2, 1985, which deals with a roller frame which surrounds a rigid frame and allows for tensioning four sides of a rectangle to place the appropriate tension upon a silk screen; and U.S. Pat. No. 5,018,442 granted to Hamu on May 28, 1991, which discloses an improvement upon the Newman patent '909 by eliminating the rigid support frame.
Patents which deal primarily with pre-forming or pre-bordering the fabric for placing upon a frame for further tensioning include: U.S. Pat. No. 5,274,934 granted to Newman, Jr. on Jan. 4, 1994, which includes strips adapted to be secured to either a fixed rectangular frame in predetermined positions or upon a roller frame for tensioning the fabric; U.S. Pat. No. 5,390,596 granted to Farr on Feb. 21, 1995, which discloses a rectangular frame which is designed so that one corner may be moved out of the plane used for screening, shortening the distance spanning the corners, then allowing the fabric to be placed on and the frame returned to its rectangular position, tensioning the fabric; U.S. Pat. No. 5,443,003 granted to Larson on Aug. 22, 1995, which discloses trimming the fabric to the configuration it will assume when under tension, placing strips or splines around the edges of the pre-cut fabric, and then snapping the fabric into place in pre-formed grooves in the roller for tensioning the fabric; and U.S. Pat. No. 5,522,314 granted to Newman, Jr. on Jun. 4, 1996, which discloses another method of accurately positioning border strips on the fabric for predetermining the appropriate position.
In addition, U.S. Pat. No. 5,488,901 granted to Hruska on Feb. 6, 1996 discloses a structure for supporting a silk screening frame and a means for placing the appropriate tension thereon.